1. Field of the Invention
The invention relates to endoscopic instruments. More particularly, the invention relates to a low friction sheath for an endoscopic instrument such as an endoscopic biopsy forceps.
2. State of the Art
Endoscopic biopsy forceps generally include a relatively long (several feet) hollow flexible member (typically a coil) with one or more flexible control members extending therethrough. The proximal ends of the hollow member and the control members are coupled to a manual actuation device for imparting reciprocal axial movement of the control members relative to the hollow member. The distal end of the hollow member is coupled to a clevis upon which a pair of biopsy forceps jaws are rotatably mounted. The distal ends of the control members are coupled to the jaws so that axial movement of the control members relative to the hollow member causes the jaws to open or close. The endoscopic biopsy forceps typically are delivered to the biopsy site through an endoscope.
An endoscope has a relatively long flexible tube carrying fiber optics and a relatively narrow lumen through which the endoscopic biopsy forceps may be inserted. The practitioner guides the distal end of the endoscope to the biopsy site and uses the fiber optics to view the site. When the distal end of the endoscope is near the biopsy site, the practitioner inserts the biopsy forceps jaws into the narrow lumen of the endoscope and pushes the long hollow flexible member through the lumen until the jaws exit the distal end of the endoscope. Since the lumen of the endoscope is narrow and the endoscope typically takes a tortuous path to the biopsy site, it is often difficult to push the biopsy forceps through the lumen to the biopsy site. Thus, the design of endoscopic biopsy forceps is often concerned with reducing friction between the outer surface of the hollow flexible member of the forceps and the interior surface of the lumen of the endoscope. For example, it is now common to provide the hollow flexible member with a shrink wrapped "TEFLON" sheath along its entire length. Such a "TEFLON" sheath is also useful for electrically insulating the hollow flexible member when the forceps are made "hot" for electrocautery.
Other endoscopic tools are often provided with a similar shrink wrapped "TEFLON" sheath for electrical insulation and/or for decreasing friction on the outer surface of the tool. "TEFLON" has been considered the ideal material for these purposes because of its high lubricity and electrical insulating properties. However, "TEFLON" is relatively expensive. Since many endoscopic instruments are made to be disposable for safety reasons, the cost of providing a "TEFLON" sheath can become significant.